Refrigerator defrosting apparatus



June 4 E. w. ZEARFOSS, JR

REFRIGERATOR DEFROSTING APPARATUS 2 Sheets-Sheet 2 Filed Sept. 8, 1950(ammo/1:74

EEE EEK Patented June 1, 1954 REFRIGERATOR DEFROSTING APPARATUS Elmer W.Zearfoss, J r., Philadelphia, Pa., assignor to Philco Corporation,Philadelphia, Pa., a corporation of Pennsylvania Application September8, 1950, Serial No. 183,757

7 Claims.

.The invention hereinafter disclosed and claimed relates torefrigeration and, more particularly, is concerned With refrigerators ofthe type having provision for automatic removal of frost deposited uponthe surfaces of the evaporator or other element used to producerefrigoration.

It is now well recognized that it is desirable to provide within arefrigerator cabinet not only a main storage compartment maintained attemperatures above the freezing point of water, in order to provide forthe proper preservation of fresh fruits, vegetables and other foodstuffswhich should not be subjected to sub-freezing temperatures, but also acompartment maintained at sub-freezing temperatures suitable for thepreservation of frozen foods over a long period of time. Commonly thelatter compartment takes the form of an enclosed rectangular evaporatormaintained at temperatures well below the freezing point of water andwhich evaporator, through the agency of air circulating throughout therefrigerator, is utilized to cool not only the space defined by itswalls but also the aforesaid main or higher temperature compartment.While such constructions have become more or less standard in theindustry they are subject to a serious disadvantage in that moisturepresent in the main higher temperature compartment is deposited upon thesub-freezing evaporator in the form of rest. Periodical removal of thisfrost is necessary in order to maintain the operating efficiency of therefrigerator, and such defrosting has frequently been accomplished byshutting down the refrigerating system. Since extended discontinuitiesof operation of the system result in thawing of frozen foods withattendant deterioration, and since the defrosting operation hasfrequently been troublesome and time-consuming, it has recently beenrecognized that automatic and relatively frequent defrosting of theevaporator is desirable. Such defrosting can conveniently beaccomplished by subjecting the evaporator to a considerable quantity ofheat over a relatively short period of time and, while such heating ofthe evaporator is not a difficult problem, the means for controlling theinitiation and duration of the defrosting operation has generally leftmuch to be desired.

A number of approaches have been made to this control problem amongwhich might be mentioned the use of timers, ratchet devices and thelike, effective to discontinue operation of the refrigeration system andapply heat to the evaporator after a predetermined period of operation.

Such devices are inherently rather complex and expensive and, inaddition, suffer from the disadvantage that defrosting cycles may beinitiated when the quantity of frost accumulated on the evaporator isnot great enough to warrant defrosting. These difficulties anddisadvantages can be overcome by the pro-vision of means automaticallyoperable to initiate and control the defrosting operation in response toaccumulation of a predetermined thickness of frost upon the evaporator,and, it is with this class of apparatus that the present invention isconcerned.

It is the primary object of my invention to provide a defrostcontrolling device which is operable in accordance with the degree offrost deposition and which is unusually simple, inexpensive andreliable. In the achievement of the foregoing general objectives, theapparatus of my invention utilizes a novel switch device which is ofsuch a nature as to be conditioned for operation by the accumulation ofa predetermined thickness of frost upon the evaporator and, when thusconditioned, is effective to energize a defrosting circuit automaticallyin response to a change in air pressure which occurs within therefrigerator cabinet under usage conditions. With more particularity,the invention is featured by the provision of means providing an airflow passage having an opening confronting the cooling unit, orevaporator, through which opening or passage air normally flows when therefrigerator door is moved, as for example when the door is closed. Aswitch element is movably mounted in the path of movement of the airwhich flows through said passage, said element being adapted to initiatethe defrosting operation when the frost upon said unit has restrictedsaid opening to an extent sufficient to prevent that degree of air flowwhich normally takes place through said passage when the refrigeratordoor is closed.

It is also an object of my invention to provide an automatic defrostcontroller which is effective to energize the defrosting circuit onlywhen the temperature conditions within the cabinet are such as towarrant subjection of the apparatus to a defrosting operation.

It is a further object of my invention to provide a defrost controllingdevice which is conditioned for operation automatically, by the merestarting of the refrigerating apparatus after shipment of the machine.

In its preferred embodiment the apparatus of this invention, brieflydescribed, comprises: means providing a pair of passages through whichair normally flows as a result of a change in air pressure occurringwithin the cabinet when the refrigerator door is closed, one of saidpassages terminating in close proximity to the cooling unit in aposition such that accumulation of a predetermined thickness of frostupon the cooling unit is effective substantially to prevent flow of airthrough the said one passage; and a movable switch member so disposed asto be contacted by the air flowing through said passages, said switchmember being actuatable--when the door to the refrigerator is closedinresponse to the resultant pressure differential created in said passagesby the aforesaid blocking of the said one passage.

The foregoing objects and features of my invention, together withcertain subordinate de tails of construction thereof are hereinafteril-- lustrated and described in the accompanying drawings in which:

Figure l is a fragmentary elevational view of a refrigerator embodyingthe invention;

Figure 2 is an enlarged view of a portion of the apparatus illustratedin Figure l, and with the controlling device of the invention shown insection;

Figure 3 is a wiring diagram illustrating certain control circuitryutilized in the apparatus of my invention;

Figure 4 is a sectional view of the control de vice, and showing saiddevice in open circuit po sition;

Figure 5 is a perspective view of the controller, partially in phantom;and,

Figure 6 is a sectional view of the controller taken generally asindicated by the line 55-5 of Figure 4.

Now making more particular reference to the drawings, and especially toFigures 1 and 2 thereof, it will be seen that the invention is thereinillustrated as embodied in a domestic refrigerator comprising an outershell is and an inner shell or liner member I l, spaced inwardly of andinsulated from the outer shell It by any suitable insulation, shown atl2. As is customary, a breaker strip i3 of low thermal conductivityextends about the forward edge of the cabinet and bridges the gapbetween the outer shell l9 and the inner liner I I. The refrigeratoralso includes a compressor-condenser unit of any desired type and, aswill be understood, this unit is connected in refrigerant flow circuitwith the evaporator shown at M. The compressor-condenser unit and therefrigerant flow conduits have been omitted from the drawings tosimplify the same, and in view of the fact that the invention is notconcerned with the refrigeration system, per se.

As clearly appears in Figure 1, inner liner member ll defines a storagecompartment l5 within the upper portion of which is disposed theaforesaid evaporator Hl, a baifle shown at l6 serving to separate theevaporator from the lower or main food storage compartment. Preferablythe baffle is of such'a nature to provide for controlled circulation ofair between the spaces above and below the same and, in this way, theevaporator I4 is utilized in cooling the entire refrigerator. As will berecognized, the evaporator 14 is subject to accumulation of frostthereon as a result of condensation of moisture present in thecirculating air.

The front access opening of the cabinet is provided with a door l'iadapted to seal the-space definedby the inner liner andseating againstcally.

Disposed intermediate the compartment 15 and ,-the lower surface ofevaporator 14 is a resistance heating element l8, saidelement beingshown diagrammatically, in the interest of simplicity in illustration.Insofar as the broader principles of the present invention areconcerned, this heater element may take a variety of forms although ametal clad type sealed against the entrance of air and -moisture hasproven very satisfactory for the purposes of the invention. The heaterelement is also included in the circuitryshown in Figure 3.

In particular accordance with the invention, the illustratedrefrigerator is provided with a novel defrost controlling switch shown,generally, at l9 and which, in the embodiment illustrated, comprises asubstantially closed housing of electrically non-conductive material,the housing being mounted in an aperture provided in a side wall ofinner liner member H and in a position such that it is disposed adjacentto the confronting side wall of evaporator H4. The housing is providedwith a laterally extending passage 20 terminating in an opening 2| whichlatter directly confronts the Wall of the evaporator in slightly spacedrelation thereto. Beneath said passage 20 the housing is provided with aplurality of openings 22, and it will be noted that the housing isfurther provided with an opening 23 through which is affordedcommunication with the space between the outer shell l0 and inner linerH.

During opening and closing movements of the main refrigerator door 11,there occurs a change in air pressure within the compartment defined byinner liner II and this pressure change is communicated to the interiorof housing l9 through the aforesaid ports or openings 2! and 22 and withresultant flow of air through said openings. Air entering the housing isoutletted through opening 23 into the insulated space between the outershell and inner liner. conditions such that there is no substantialaccumulation of frost upon the evaporator, and as will be understood bya consideration of the arrows representing air flow, in Figure 4, thereis a flow of air, when the main door is closed, inwardly through opening2! and thence through opening 23, and also inwardly through the openings22 and out of the aforesaid opening 23.

Returning now to a consideration of the controlling device, per se, itwill be seen that the conductive housing is provided with a pair ofscrew threaded adjustable contact elements 24-24 which, together with 'anovel pivoted switch member 25, comprise the switch which initiates andcontrols the defrosting operation. As clearly appears in Figure 5, themajor portion of housing I9 is circular in cross-sectional shape and thepivoted switch element or blade 25 is circular in plan and extendshorizontally through the housing at a level intermediate the level ofthe openings-2i and 22. Preferably, although not necessarily, this bladeor element comprises a bi-metal disk of known type which disk, inresponse to changes in temperature, is adapted to 1 have its midportionmove over center with a snap action. The disk is pivotally mounted, asat 26 (Figure 5), near thatedge Which is disposed advjacentto passage 20and is thus mounted with Under freedom for movement between a loweropencircuit position, illustrated in Figure 4, and an uppercircuit-closing position shown in Figure 2. Means is provided releasablyto retain the disk in the upper position, this means taking the form ofa small permanent magnet 2'1 mounted for vertical adjustment movementsthrough the agency of a screw threaded shaft 28. For a pirpose whichwill appear more fully hereinafter the housing It is also provided witha downwardly extending screw threaded member 29 which comprises a stoplimiting the upward movement of the disk and providing a reaction usedwhen the disk snaps over center. This stop 29 appears in Figure 5. Anupwardly extending adjustable stop element til limits the downwardmovement of the disk 25.

Defrosting is automatically initiated, as and when required, in responseto accumulation of frost upon the evaporator M. A coating of frost isrepresented at 3! in Figure 2 and, as clearly appears from the figure,the frost has accumulated to a thickness such as to block off theopening 2| in passage 2%. After frost has accumulated to the extentshown, the next succeeding closing movement of the main door ll resultsin flow of air through the lower apertures 22 and outwardly of the exitport 23, but no flow takes place through the upper opening 2 i.

As will be understood by a comparison of Figures 2 and 4, the pressurevariation which occurs within the cabinet when the door I! is closed,and under conditions such that there is little if any frost accumulationupon the evaporator, results in subjecting the portions of the housingI!) which lie above and below the disk 25 to substantially the samepressure and, accordingly, air flows through the ports 22, as well asthrough the opening 2i, inwardly of the housing and is outletted throughthe exit opening 23. Under such conditions there is no substantialdifference of pressure across the switch disk 25 and, consequently, thedisk remains in its lower or normal position. When, on the other hand,frost has accumulated to the extent illustrated in Figure 2, theblocking off of opening 2! results in a difference of pressure beingapplied across the disk 25, that is, unequal pressures are applied tothe opposite faces of said disk, with the result that air movinginwardly through the openings 22 raises the pivotally mounted disk 25 tothe position shown in Figure 2, in which position the disk bridges thecontacts 2-t2 and thus initiates the defrosting operation. As indicatedhereinabove the disk is releasably retained in this uppercircuit-closing position by the permanent magnet 27.

Under normal operating conditions of the refrigerator, the temperatureof the bi-metal disk, due to its proximity to the evaporator, willassume a value within a range dependent upon the temperature of theevaporator, the spacing between the evaporator and the controllingdevice, the effectiveness of the cabinet insulation, and like factors.In one representative embodiment which has given good results inpractice, the tem perature of the bi-metal disk under normalrefrigeration conditions is 25 F., or somewhat below that value, Thedisk is so calibrated that, under such conditions, it presents a concaveside upwardly and as a result, when the disk is moved to its upperposition (as a result of closing of the door and accumulation of frostsufiic-ient to block opening 2!) the center portion of the disk does notstrike the upper limiting stop 29 and the edge portions of the diskbridge the contacts z t-24 with the result that the defrosting circuitis made. In any particular design there is also a disk temperature whichcorresponds to completion of the defrosting operation, that is, atemperature which the disk attains when the coating of frost has beencompletely removed. In the illustrated embodiment this temperature is inthe region of 58 F. When, due to the heat applied to the evaporator toefiect defrosting, the disk reaches this upper control temperature itsnaps over center to a condition in which the side which confronts thecontacts 2424 is covex. As a result, and during such over centermovement, the midportion of the disk reacts against the centrallylocated upper stop element 29 and effects movement of the disk to itslower position, with resultant opening of the defrosting circuit. As theevaporator regains its normal operating ternperature the disk, while insaid lower position, again moves over center to present a concave sideupwardly, thus being reset in position such as to enable it to bridgethe contacts 2t2 l when the next defrosting cycle is initiated. Thedisk, of course, remains in the lower position until such time as thefrost has again accumulated to a degree such that closing of the doorresults in an appreciable pressure difference across the disk, at whichtime the latter is again moved to its upper position to repeat thedefrosting cycle above described.

While the use of a bi-metal disk is preferred, it is to be borne in mindthat, in the broader aspect of the present invention, other switchblades or elements might be employed. For example, the bi-meta1 diskmight be replaced by a simple metal leaf, provision being made forcontrol of the defrosting circuit by momentary contact. Similarly, Whilethere are advantages in designing the apparatus to operate in accordancewith the difference of pressure created within the cabinet when the dooris closed, the pressure difference which occurs when the door is openedcould also be employed to control the position of the disk, withoutdeparture from the essential and broader concepts of the invention.

While the constructional principles and operational features of theinvention will be understood from the foregoing description, a briefdescription of the control circuitry may to advantage be set forth.Respecting the wiring diagram (Figure 3), there is diagrammaticallyillustrated therein the controller l 9, the resistance heater it, anoverload protective device of known type, shown at 32, a motorcompressor 33 and a conventional temperature cycle-control St, togetherwith an associated bulb 35 responsive to the temperature of theevaporator it.

Under normal operating conditions of the refrigerator, current from theleft side of the supply line 36 flows through a heater coil 3? arrangedin high heat conducting relation with respect to a bi-metallic overloadprotective blade 38, through the contacts associated with said blade,through the compressor 3, the cyclically operable temperature controlswitch 35, and thence to the other side of the line. As will berecognized, this is common practice.

When defrosting is required, the compressor may or may not be inoperation. Assuming that the compressor is in operation, a circuit iscompleted through the contacts of the controller iii, in the manneralready described and, under these conditions there is a division ofcurrent flowing through the heater winding 31, part of the currentflowing through the bi-metallic blade 38 and the compressor, asdescribed, and a portion of the current flowing through the defrostheating coil I8 and thence returning to the other side of the line. As aresult of the fact that the defrosting coil l8 draws considerable power(for example, 660 watts) the surge of current through the heater coil 31of the overload protective device is suiiicient to open the contacts ofthe bimetallic blade 38 and to maintain them in open position throughoutthe defrosting operation. Thus the compressor, if it be in operationwhen defrosting is initiated, is shut off and remains off until thecontacts in the controller [9 are again opened at the termination of thedefrosting operation. When the latter contacts reopen, cooling of theheater coil 31 resets the blade 36 and provides for normal cycling ofthe refrigeration system.

In the event that upward movement of the disk 25 should occur when therefrigeratordue perhaps to abnormally heavy usage-is at a temperature soelevated as to make it undersirable to subject the apparatus to adefrosting operation, the disk 25, as a result of such abnormally hightemperature, will present a convex side upwardly toward the contacts2424 and, the convex side bears against the stop member 29; although thepermanent magnet will retain the disk in said upward position thedefrosting circuit will not be closed. Upon restoration of normaltemperature conditions the disk, as set forth above, moves over center,without dropping to its lower position, so that the face which confrontsthe contacts is concave and the contacts are thu closed to permit thedefrosting operation to take place. As above indicated the disk moves toits lower position, after defrosting is completed, to be reset by pulldown of the temperature of evaporator M.

During shipping, or other movement of the refrigerator, the disk mayinadvertently be moved toward its associated contacts and held in. thatposition by the permanent magnet 27. A a. result of the high ambienttemperature normally encountered when the apparatus is not in operation,for example during shipment, a convex side of the disk is presentedtoward the contacts and the circuit is therefore not closed immediately.Upon attainment of normal refrigerating temperatures the disk moves overcenter and the defrosting circuit is completed. While the defrostingoperation which may be initiated under such circumstances may not beentirely necessary it will be of very short duration, due to the rapidrise in evaporator temperature which takes place in the absence of acoating of frost, and normal operation of the box is thereforeestablished in a short period of time as soon as the disk has reachedthe upper control temperature limit (50 F.).

From the foregoing description'it will be understood that'by the presentinvention there is provided not only a new and useful refrigerator inwhich air pressure changes occurring within. the cabinet are utilized toprovide direct and highly reliable indication and control of thequantity of frost present upon the evaporator, but also that theinvention has provided a novel switch device characterized by unusualsimplicity and low cost.

While the foregoing specification'is concerned with a singlerepresentative embodiment, itwill be understood that the invention issusceptible of change and modifications without departing fromtheessential concepts thereof. For example, and in the broadest aspectof the invention; the changes in cabinet air temperature which areutilized to actuate the control switch need not necessarily take placeas a result of movement of the refrigerator door. Changes in airpressure could be brought about by other means such as a periodicallyoperable diaphragm. Use of the door for this purpose is highlyadvantageous and is therefore to be preferred, but certain importantadvantages of the invention may be realized without such use. It will berecognized, however, that the invention contemplates changes andmodifications which come within the terms of the appended claims.

I claim:

1. In a refrigerator, an inner liner member defining a storagecompartment having an access opening, a door normally closing saidopening,

a cooling unit within said compartment and upon which frost accumulatesduring normal operation of the refrigerator, means providing a pair ofpassages leading through a wall portion of said inner liner member andthrough which passages air flows as a result of change of pressureoccurring within said compartment when the door is closed, one of saidpassages terminating in close proximity to the cooling unit in aposition such that accumulation of a predetermined thickness of frostupon the cooling unit is effective substantially to prevent flow of airthrough the said one passage, and a movable switch member so disposed asto be contacted by the air flowing through said passages, said switchmember being actuatable, when the door to the refrigerator is closed, inresponse to the resultant pressure differential created in said passagesby blocking of the said one passage by the stated accumulation of frost.

2. In refrigerator apparatus, a cabinet defining a storage compartmentand including a door, means for cooling said cabinet and includingsurface portions disposed therewithin and subject to frost accumulationduring normal operation of the apparatus, means periodically operable todefrost said surface portions, and means responsive to the thickness ofaccumulated frost to initiate operation of said defrosting means, saidlast means including: a housing and passage means communicating with thespace within said compartment and with the space outside thereof,cabinet air tending to flow through said passage means, into saidhousing and thence into the space outside said compartment in responseto closing of the door; and a switch element and associated contactswithin said housing, said switch element being movable between an openposition in which the defrosting means is not energized and a closedposition in which said defrosting means is energized, said passage meansincluding a portion so disposed as to be closed by the accumulation of apredetermined thickness of frost on said surface portions, withresultant change in the flow of cabinet air which normally occurs duringthe closing of said door, and said switch element being so constructedand arranged as to move to a closed position with respect to theassociated contacts when the passage means has thus been closed.

3. Refrigerator apparatus in accordance with claim 2, and furthercharacterized in that said switch element comprises a bi-metallicthermosensitive member, a portion of which is movable with a snap actionwith respect to another portion thereof, in response to an increase intemperature of said cooling means, to reset said switch element byeffecting movement of the same to the stated open position.

4. In a refrigerator including a door, the combination of: a coolingunit upon which frost accumulates; means providing an air flow passagehaving an opening confronting the cooling unit and through which openingand passage air flows when the refrigerator door is moved; a switchelement pivotally mounted in the path of air flowing through saidpassage and eifective to initiate a defrosting operation when the frostupon said unit has restricted said opening to degree sufiicient toprevent substantial flow of air through said passage in response tomovement of said door, thereby causing pivotal movement of said switchelement from an open-circuit position to a circuit closing position,said switch element comprising a bi-metallic member a portion of whichis movable with a snap action with respect to another portion thereof inresponse to thermal changes occurring within said refrigerator; and stopmeans against which said switch element may react, during the said snapaction movements, to cause pivotal movement of said member back to itsopen-circuit position.

5. In a refrigerator including a compartment provided with a door, thecombination of a cooling unit within said compartment and upon whichfrost accumulates during normal operation of the refrigerator, structureproviding air flow passage means having an opening confronting thecooling unit and an opening in communication with space outside of saidcompartment,

and through which openings and passage means air normally flows when therefrigerator door is moved, and a switch member movably mounted in thepath of movement of air flowing through said passage means, said memberbeing effective to initiate a defrosting operation when the frost uponsaid unit has restricted said opening to a degree sufficient to preventsubstantial flow of air through said passage means in response tomovement of said door.

6. In a refrigerator, a storage compartment having an access openingnormally closed by a door, means presenting a cooling surface withinsaid compartment and upon which frost accumulates during normaloperation of the refrigerator,

means providing a pair of passages leading out- 1 side said compartmentand through which passages air flows as a result of change in pressureoccurring within said compartment when the door is closed, one only ofsaid passages terminating in close proximity to said cooling surface ina position such that accumulation of a predetermined thickness of frostupon said surface is effective substantially to prevent flow of airthrough the said one passage, and a movably mounted switch member sodisposed as to be contacted by the air flowing through both of saidpassages, said member being adapted to remain in open-circuit positionunder conditions such that air flows through both said passages, frostblockage of the said one passage serving to prevent flow of air throughthat passage and to efie'ct movement of said member to a circuit closingposition.

7. In a refrigerator having a compartment including an evaporator andprovided with a door, closure of said door effecting a transientincrease in air pressure within said compartment, means defining apassageway within said compartment, said passageway normally being inopen communication with the interior of said compartment and with spaceoutside thereof, a movably mounted member disposed within saidpassageway and dividing the same into parallel passage portions, theinner end of one passage portion being disposed adjacent saidevaporator, air normally being free to escape from said compartmentthrough both passage portions in parallel in response to closure of saiddoor, frost accumulation upon said evaporator preventing such flow ofair through said one passage portion, and thereby causing movement ofsaid memher when the door is closed and said one passage portion isblocked.

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